[Show abstract][Hide abstract] ABSTRACT: The helicity structure of the diffractive electroproduction of rho mesons, e + p --> e + rho + Y, is studied in a previously unexplored region of large four-momentum transfer squared at the proton vertex, t: 0 < t' < 3 GeV2, where t' = \t\ - \t\ min. The data used are collected with the HI detector at HERA in the kinematic domain 2.5 < Q(2) < 60 GeV2, 40 < W < 120 GeV No t dependence of the r(00)(04) spin density matrix element is found. A significant t dependent helicity non-conservation from the virtual photon to the rho meson is observed for the spin density matrix element combinations r(00)(5) + 2r(11)(5) and r(00)(1) + 2r(11)(1). These t dependences are consistently described by a perturbative QCD model based on the exchange of two gluons. (C) 2002 Elsevier Science B.V. All rights reserved.
Physics Letters B 07/2002; 539:25-39. DOI:10.1016/S0370-2693(02)02035-X · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: ANTARES is a project leading towards the construction and deployment of a neutrino telescope in the deep Mediterranean Sea. The telescope will use an array of photomultiplier tubes to detect the Cherenkov light emitted by muons resulting from the interaction with matter of high energy neutrinos. In the vicinity of the deployment site the ANTARES Collaboration has performed a series of in situ measurements to study the change in light transmission through glass surfaces during immersions of several months. The average loss of light transmission is estimated to be only ∼2% at the equator of a glass sphere one year after deployment. It decreases with increasing zenith angle, and tends to saturate with time. The transmission loss, therefore, is expected to remain small for the several year lifetime of the ANTARES detector whose optical modules are oriented downwards. The measurements were complemented by the analysis of the 210Pb activity profile in sediment cores and the study of biofouling on glass plates. Despite a significant sedimentation rate at the site, in the 0.02–0.05 cm yr−1 range, the sediments adhere loosely to the glass surfaces and can be washed off by water currents. Further, fouling by deposits of light-absorbing particulates is only significant for surfaces facing upwards.
[Show abstract][Hide abstract] ABSTRACT: A search for contributions to the reaction ep→eπ0N∗ from photon–odderon fusion in the photoproduction regime at HERA is reported, at an average photon–proton centre-of-mass energy 〈W〉=215 GeV. The measurement proceeds via detection of the π0 decay photons, a leading neutron from the N∗ decay, and the scattered electron. No π0 signal is observed and an upper limit on the cross section for the photon–odderon fusion process of σ(γp→π0N∗)<49 nb at the 95% confidence level is derived, integrated over the experimentally accessible range of the squared four-momentum transfer at the nucleon vertex 0.02<|t|<0.3 GeV2. This excludes a recent prediction from a calculation based on a non-perturbative QCD model of a photon–odderon fusion cross section above 200 nb.
Physics Letters B 06/2002; 544:35-43. DOI:10.1016/S0370-2693(02)02479-6 · 6.13 Impact Factor